1. Field of the Invention
The present invention relates to a coating and developing system including a coating unit for coating a surface of a semiconductor wafer (hereinafter, referred to simply as “wafers”) with a resist film and a developing unit for developing the resist film processed by immersion exposure by using a developer, and a coating and developing method.
2. Description of the Related Art
A photoresist pattern forming process, namely, one of semiconductor device fabricating processes, includes the steps of forming a resist film on a surface of a wafer by applying a resist to the surface of the wafer, exposing the resist film in a predetermined pattern, and developing the exposed resist film by using a developer to form a resist pattern. Generally, this photoresist pattern forming process is carried out by a system built by connecting an exposure system to a coating and developing system including a coating unit and a developing unit.
A wafer is transferred, for example, through an interface block interposed between the coating and developing system and the exposure system from the coating and developing system to the exposure system and from the exposure system to the coating and developing system. An interface block provided with two carrying arms is mentioned in Patent document 1. The two carrying arms cooperate to transfer a wafer between the coating and developing system and the exposure system.
An immersion exposure method has been studied in recent years to improve exposure resolution to cope with the progressive fining of device patterns and the progressive thickness reduction of films. The immersion exposure method coats a resist film formed on a surface of a wafer with a transparent liquid layer, such as a layer of ultrapure water, and exposes the resist film formed on surface of the wafer through the liquid layer to light emitted by a light source to form a predetermined latent circuit pattern in the resist film. Immersion exposure utilizes the characteristic of light that the wavelength of light shortens in water. For example, the wavelength of ArF light shortens from 193 nm in air to about 134 nm in water.
When a liquid layer is formed on the surface of a resist film for immersion exposure, the resist is likely to be eluted by the liquid layer during the photoresist pattern forming process. An eluate containing the resist eluted by the liquid layer is likely to adsorb particles. The liquid forming the liquid layer remain on the wafer W after the exposure process. If the eluates containing the resist remain on the wafer W, particles may be produced on the surface of the wafer. When the wafer contaminated with particles is transferred from the exposure system to the carrying arm of the interface block, the carrying arm will be contaminated with the particles. Then, other wafers carried by the contaminated carrying arm will be contaminated with the particles.
When a wafer contaminated with particles in the exposure process or a wafer carried by the carrying arm contaminated with particles is carried to the coating and developing system, the particles sticking to the wafer stick to, for example, the carrying arm of the coating and developing system. The carrying arm contaminated with particles scatters the particles in a processing unit and contaminates other wafers with particles. Consequently, it is likely that the coating and developing system is contaminated entirely with particles. When a wafer contaminated with particles is subjected to heating process, parts contaminated with particles of the wafer and those not contaminated with particles are heated at different temperatures, respectively. Particularly, in a heating process for diffusing an acid catalyst produced during exposure in a resist film of a chemically amplified resist, particles adhering to the resist film affect the line-width of the resist pattern greatly. Moreover, particles adhering to the wafer are likely to damage the resist pattern during the developing process.
If contamination with particles (hereinafter, referred to as “particle contamination”) spreads in the coating and developing system and a heating unit is used for processing a wafer both before and after the exposure process, a wafer to be transferred through the heating unit to the exposure system will be contaminated. Particles are transferred from the carrying arm to a wafer being carried to the exposure system as well as to a wafer being carried out of the exposure system. Therefore, particles may be accumulated in the exposure system. When the exposure system carries out an immersion exposure process, particles migrating in a liquid layer in an exposed area obstruct normal exposure. Consequently, an accurate resist pattern cannot be formed and defects in the resist pattern are likely to be distributed on the wafer.
Formation of water marks is another problem other than that of particle contamination in immersion exposure. Water marks form when a liquid used for immersion exposure and remaining on a wafer is dried due to the solidification of solids dissolved in the liquid. Water marks will obstruct the normal processing of a wafer by an exposure process. Any measures to deal with those problems are not mentioned in Patent document 1. Patent document 1: JP-A No. 2004-193597